Ganong's Review of Medical Physiology, 23rd Edition

274
SECTION III
Central & Peripheral Neurophysiology

(see Figure 15–5). Paraventricular neurons that probably secrete
oxytocin and vasopressin project in turn to the hindbrain and
the spinal cord. Neurons that secrete epinephrine have their cell
bodies in the hindbrain and end in the ventral hypothalamus.
An intrahypothalamic system of dopamine-secreting neu-
rons have their cell bodies in the arcuate nucleus and end on
or near the capillaries that form the portal vessels in the
median eminence. Serotonin-secreting neurons project to the
hypothalamus from the raphe nuclei.

RELATION TO THE PITUITARY GLAND

There are neural connections between the hypothalamus and
the posterior lobe of the pituitary gland and vascular connec-
tions between the hypothalamus and the anterior lobe. Embry-
ologically, the posterior pituitary arises as an evagination of the
floor of the third ventricle. It is made up in large part of the end-
ings of axons that arise from cell bodies in the supraoptic and
paraventricular nuclei and pass to the posterior pituitary (Fig-
ure 18–2) via the
hypothalamohypophysial tract.
Most of the
supraoptic fibers end in the posterior lobe itself, whereas some
of the paraventricular fibers end in the median eminence. The
anterior and intermediate lobes of the pituitary arise in the em-
bryo from the Rathke pouch, an evagination from the roof of
the pharynx (see Figure 24–1). Sympathetic nerve fibers reach
the anterior lobe from its capsule, and parasympathetic fibers
reach it from the petrosal nerves, but few if any nerve fibers pass
to it from the hypothalamus. However, the
portal hypophysial

FIGURE 18–1
Human hypothalamus, with a superimposed diagrammatic representation of the portal hypophysial vessels.

Dorsal hypothalamic area

Paraventricular nucleus

Anterior hypothalamic area

Preoptic area

Supraoptic nucleus

Suprachiasmatic nucleus

Arcuate nucleus

Optic chiasm

Median eminence

Superior hypophysial artery

Portal hypophysial vessel

Anterior lobe Pituitary

gland

Posterior lobe

Primary

plexus

Posterior hypothalamic nucleus

Dorsomedial nucleus

Ventromedial nucleus

Premamillary nucleus

Medial mamillary nucleus

Lateral mamillary nucleus

Mamillary body

FIGURE 18–2

Secretion of hypothalamic hormones.

The hor-

mones of the posterior lobe (PL) are released into the general circulation

from the endings of supraoptic and paraventricular neurons, whereas

hypophysiotropic hormones are secreted into the portal hypophysial

circulation from the endings of arcuate and other hypothalamic neu-

rons. AL, anterior lobe; MB, mamillary bodies; OC, optic chiasm.

MB

OC

PL

Supraoptic and

paraventricular

nuclei

Arcuate

and other

nuclei

AL

Anterior

pituitary hormones

Posterior pituitary

hormones